The present application relates to and incorporates herein by reference Japanese Patent Application No. 11-75888 filed on Mar. 19, 1999.
The present invention relates to wireless communication systems and method in which a plurality of different types of communication networks operable under different communication protocols are integrated to enable communications between different types of communication devices.
Mobile communication systems presently used include various communication networks such as an FDMA network operable under a frequency division multiple access (FDMA) protocol, a TDMA network operable under a time division multiple access (TDMA) protocol, a CDMA network operable under a code division multiple access (CDMA) protocol, a cordless phone network and the like. The CDMA network is considered more promising than the FDMA network and the TDMA network, because its provides the highest efficiency with respect to frequency utilization. The CDMA network has its own service area which is more limited than those of the FDMA network-and the TDMA network.
It is therefore proposed to provide dual-type cellular phones which are compatible with the CDMA communication protocol and other communication protocols. The cellular phone of this kind operates under the CDMA protocol for communication with other phones as long as it is inside a service area of the CDMA network. The cellular phone operates under the other communication protocol for communication with other phones as long as it is outside the service area of the CDMA network.
The CDMA network has a global positioning system (GPS) receiver at its radio communication cell station to receive a GPS time signal transmitted from a GPS satellite. The received time signal is used to correct system operation synchronization time of the CDMA network based on the GPS time. Thus, the system operation time of the CDMA network can be synchronized very accurately, because the GPS time is very accurate.
Some of the other communication networks use a network synchronization method. That is, those networks correct respective system operation synchronization times based on the reference time of a public communication network which comprises a public switched telephone network (PSTN), an integrated services digital network (ISDN) or the like. The reference time provided in those networks is less accurate than that of the GPS time, and hence the accuracy in synchronizing the system operation time is not high enough. If it is desired to increase the accuracy in synchronizing the system operation times in communication networks other than the CDMA network, GPS receivers are necessitated at the cell stations of those communication networks. The GPS receivers in those other networks thus cause an increase in cost and are not practical.
It is therefore an object of the present invention to provide a wireless communication which is capable of increasing the accuracy in synchronizing system operation time.
According to the present invention, an integrated communication system is constructed with a plurality of communication networks operable under different communication protocols. The communication networks includes a first network such as a CDMA network and a second network such as a private cordless phone network. The first network receives a GPS time signal from a GPS satellite and transmits a GPS-synchronization signal in synchronism with the GPS time signal. When a cellular phone receives an output request signal such as a position registration request signal from the second network, it transmits an output signal such as a position registration-signal to the second network at a time synchronized with the GPS-synchronization signal. The second communication network responsively corrects a time of synchronization of its operation time based-on the received output signal. As the GPS time signal is generated accurately, the second communication network is enabled to correct its operation time accurately.